The tracks area is where the actual editing happens. You can define up to three text track, three video and three audio tracks in a project. To start editing, drag a video from the Media List and drop it to the track matching the media. Then you can move it left and right to put it into the right position on the timeline. 

Above the tracks, to the left you can enable magnet so dragged clips are snapped to the nearest clip or start/end of the video and zoom in or out the viewport.

Select several clips at the timeline by pressing down Ctrl (Cmd on Mac) and selecting the individual clips. You can now move several clips at the timeline.

Each text and video track can be hidden so you can check various combinations of clips before rendering the final video. Whole audio and video tracks can be muted so you can completely remove the original sound and replace it with a music or sounds from another video. Also individual clips can be muted or turned the volume down from the Edit clip window.

Waveforms

New videos and audio files added to the media library will have waveforms visualized when added to a track in the video editor. This will make editing easier, for example when editing transitions to be in sync with a beat in an audiotrack added to the project.